Compact gain measurements on reflector antennas

The paper describes an extremely compact method of making gain measurements on parabolic reflector antennas. The concept involves making return-loss measurements on the antenna when it is located in front of a plane reflecting screen mounted parallel to the antenna aperture. This compact configuration is convenient for laboratory measurements or factory testing and has been used on reflectors of up to 12 ft (3.66 m) in diameter (in the latter case, employing a water bath to represent the plane flat reflecting surface). The return-loss measurements provide information on the various loss mechanisms which degrade the normal operation of an antenna, and the paper provides a detailed experimental and theoretical study of such losses and their relation to the measurement system. The results show an accuracy of the order of 0.1 dB for gain measurement, aided by the fact that the system corresponds to a 2-way (transmit-and-receive) measurement on the antenna. The paper discusses various ways of using the measurement for comparative and absolute determination of antenna gain.